The complement system is activated via three distinct pathways; the classical pathway, the lectin pathway and the alternative complement pathway (AP). The classical pathway is activated via antigen-antibody complexes. The lectin pathway is a variation of the classical pathway and the alternative pathway is activated by foreign material, artificial surfaces, dead tissues, bacteria, dead yeast cells.
The classical complement pathway is important for host defense against pathogens. Activation of the classical pathway generates C3a, C4a, C5a and C5b-9 molecules, which activates a variety of cells in response to host defense. In pathological conditions, as a result of activation of the alternative pathway, anaphylatoxins C3a, C5a are formed and tissues damaging C5b-9 molecules, also known as the membrane attack complex (MAC), are formed. These molecules mediate inflammation via cellular activation and release of inflammatory mediators. In addition to its role as a lytic pore-forming complex, there is strong evidence that the depositing of sublytic MAC may play an important role in inflammation.
The alternative complement pathway is activated in pathological inflammation. Elevated levels of C3a, C5a, and C5b-9 have been found associated with multiple acute and chronic disease conditions. These inflammatory molecules activate neutrophils, monocytes and platelets. Therefore, inhibition of disease-induced AP activation is important for clinical benefit in the diseases where complement activation plays a role in disease pathology.
In addition to its essential role in immune defense, the complement system contributes to tissue damage in many clinical conditions. The activities included in the complement biochemical cascade present a potential threat to host tissue. An example includes the indiscriminate release of destructive enzymes possibly causing host cell lysis. Thus, there is a pressing need to develop therapeutically effective complement inhibitors to prevent these adverse effects.
In a disease condition where AP activation contributes to disease pathology, elevated levels of C3a, C5a and C5b-9 molecules are found in serum, plasma, blood or other body fluids representative of the disease. Production and inhibition of each of these molecules via different mechanisms is important for diseases. One possible mechanism for inhibiting the formation of active C3 convertase is via the use of an anti-C3b antibody. Thus blocking/inhibiting or preventing AP activation via depleting C3b, neutralizing C3b, C3c or inactivating C3b remains an important therapeutic strategy.
The application developed humanized and chimeric antibody sequences that are novel and provide targeted binding to C3b. The binding of C3b to B, and not C3b to C5, is inhibited by this antibody. C3a, C5a, and C5b-9 all drive inflammation and also amplify the AP activation process. Anti-C3b agents that bind C3b and prevent B interaction include but not limited to monoclonal and polyclonal antibodies, chimeric, humanized, fully human, and nano-antibodies, Full length and fragments thereof including IgG, Fab, Fab′, F(ab′)2, and IgGs. Apatamers, small molecules, and SiRNA can also neutralize C3b binding to B and prevent production of AP induced production of C3a, C5a, and C5b-9. As a result, cellular activation, inflammation and release of inflammatory mediators are also prevented. Because AP activation is linked to various acute and chronic human diseases, the blockade with anti-C3b agents will also block the inflammation process providing clinical benefit to mammals treated with the anti-C3b monoclonal antibodies.
Complement is one of several factors involved in pathogenesis and could be a significant pathological mechanism that offers an effective point for clinical control. The need for effective complement inhibitory drugs is signified by growing recognition of the importance of complement-mediated tissue injury in a variety of disease states. Despite this, currently there is a complete absence of approved drugs for human use that specifically target and inhibit complement activation.
Based upon the available clinical and research data, it appears that in most acute and chronic settings, production of C3a and C5a is mediated by the activation of the complement pathways. In clinical settings, both C3a and C5a have been independently shown to be involved, developing suitable methods of inhibition for all pathways would be highly desirable. Both of the anaphylatoxins C3a and C5a are known to activate leukocytes and platelets. A frequent indicator of cellular activation is the cellular expression of CD11b on leukocytes, and CD62P on platelets. The release of several inflammatory molecules is triggered by the platelet-leukocyte binding mediated by these activation markers. One result of such conjugate formation is the removal of platelets from the circulation, a phenomenon that can contribute to the development of thrombocytopenia.
This invention is designed to inhibit the functional activity of C3b and its progressive effects in pathological conditions by use of an anti-C3b antibody.